1. Field of the Invention
The present invention relates to a method and an apparatus for controlling a solenoid actuator in a proportional integral and differential control mode.
2. Description of the Prior Art
It is well known that an effective method for controlling the position of, for example, various regulating members for internal combustion engines by means of a solenoid actuator, stably and with excellent response charactaristics is to control the amount of operation of the solenoid actuator in a proportional integral and differential (PID) control mode and to determine the appropriate constant for the PID control in accordance with the characteristics of the solenoid actuator. U.S. Pat. No. 4,603,668 discloses an improved method of this type, in which the control performance is further enhanced by determining each constant used for PID control in accordance with the difference between the target amount and the actual amount of the operation of the solenoid actuator.
However, the resistance value of the solenoid coil of the actuator depends upon a temperature and, therefore when the temperature of the solenoid actuator varies, the level of the current flowing through the solenoid coil may be shifted from the appropriate design value even if the voltage applied to the solenoid coil is constant. As a result, the dynamic control characteristics, in particular the step response characteristics, of the control of the solenoid actuator may be markedly changed. Thus, in the case where the temperature of the solenoid actuator varies for some reason, the values of the constants used for the PID control operation are shifted from the appropriate value, so that the dynamic characteristics, particularly the stability and/or the response characteristics may be degraded.